The Colorado DOT (CDOT) is holding the ultimate cage match. It has pitted asphalt against concrete in a real-life test.
The question often asked when road construction decisions are being made is: Are asphalt and concrete equally suitable for heavily traveled roads and intersections? As part of its continuing effort to improve construction methods, CDOT is comparing the pros and cons of hot-mix asphalt (HMA) and portland cement concrete pavement (PCCP).
To make a valid comparison, CDOT has placed both surfaces side by side—exposed to the same weather, soil, and travel conditions. The ultimate goal is to better understand construction and maintenance costs, performance, and overall applicability of the two pavement types. The data also will help engineers decide between HMA and PCCP when designing highway projects.
The Long-Term Performance Monitoring of Asphalt and Concrete Pavements Study was initiated in 2002, coinciding with the start of construction on a project that would build a much-needed four-lane expressway through Colorado Springs, Colo.
“Powers Boulevard was selected because it's a brand new road and we anticipate similar traffic counts in both directions,” says CDOT's Mark Andrew, resident project engineer. “This allowed us to build the northbound segment with concrete and southbound segment with asphalt. We constructed 3 miles, giving us a section that's long enough to gather sufficient information over a variety of elevations to assess the life cycle of both surfaces.”
ROUND ONE—AND BEYOND
CDOT engineers determined a 10- to-15-year time frame would be required to establish the study's validity, allowing for enough data to be collected in a variety of circumstances, including the seasonal and wide temperature variations that occur in Colorado. To verify the data, weigh-in-motion (WIM) stations were installed on both the concrete and asphalt segments of the new expressway.
“Pavements are designed to carry finite amounts of traffic, so performance greatly depends on how much traffic is using a particular segment,” says CDOT Materials Engineer Richard Zamora. “This site was selected as an evaluation section for asphalt and concrete because of its virgin alignment, and our expectation that traffic numbers will be comparable between northbound and southbound Powers Boulevard. WIM stations were included on this project to verify this assumption and to make sure we're not comparing apples and oranges when evaluating the performance of the asphalt and concrete sections.”
Testing will take place annually. The projected cost of the study is about $12,000 per year, mostly to cover research salaries for data collection and analysis. The study is funded with CDOT's State Planning and Research money, which allocates funds to proposed studies based on the prioritization of the project.
“We'll analyze how the two surfaces are rutting at selected intervals, if there's cracking and why it's occurring, and how the smoothness of asphalt and concrete compare over several years,” Zamora says. “We also want to know how skid numbers differ on both surfaces. We'll get some of that data by suddenly stopping vehicles with ribbed tires at 40 mph.”
CDOT's research branch is seeking additional sites to perform similar side-by-side comparison studies. In addition to Powers Boulevard, CDOT is conducting related analysis at four intersections along one highway segment in the Denver area. It involves testing asphalt at two intersections and concrete at the other two.
As part of its continuing comparison analysis of concrete and asphalt, performance information will be collected periodically over the length of these studies. Engineers then will produce reports every five years and a final report documenting the entire research effort at the end of the study. What will it tell highway engineers in 2015 or 2020?
Inquiring minds will be ready to know.
— Wilson is CDOT's public relations manager.
Tests will compare pavement noise levels
Like all transportation departments, the Colorado DOT (CDOT) deals with complaints about pavement noise. In addition to comparing the long-term performance of concrete vs. asphalt, CDOT is comparing pavement noise on the standard longitudinally tined concrete pavement (tining) and asphalt.
“This will give us the additional information we need to help our decision-making process,” says Richard Zamora, CDOT materials engineer. The qualities of both materials have been debated for years, and the results will help CDOT determine life-cycle costs and benefits. Information collected on this project will educate the CDOT on how to most effectively spend its limited budget.